1. Field of the Invention
This invention relates to a new process for recovering shale oil from raw oil shale. More particularly, the invention relates to a new process for treating raw oil shale using a new integrated hyrogenation/thermal pyrolysis process involving the addition of pulverized coal which produces oil which is more characteristic of typical crude oil as well as supplemental gas and coal char fuel.
Specifically, the invention provides a new and improved process for recovering oil from raw oil shale using a new integrated hydropyrolysis/thermal pyrolysis technique and involving the addition of pulverized coal which produces a combined oil product which is more characteristic of typical crude as well as supplemental gas and coal char fuel and has unusually low heat and energy requirements, which process comprises passing hot crushed and ground raw shale to a slurry mixer where it is mixed with hot recycle oil, treating the resulting slurry with hydrogen under elevated temperature and pressure for a short period, discharging the resulting mixture to a product stripper wherein the product hydrocarbons and a portion of the recycle slurry oil is vaporized and passed to a separation column where the desired fractions are removed and heavy gas oil recovered, mixing a portion of the heavy gas oil with pulverized coal particles to form a pumpable coal slurry, passing the slurry and remaining slurry oil from the product stripper to the top of the thermal retort which is operated under fluidized bed conditions such that a temperature gradient is maintained by introducing spent shale and coal char that has been burned in an air lift combustor at two or more different treatment zones, the upper zone being selected such that the temperature is sufficient to vaporize the remaining slurry oil, and the lower zone being selected such that the temperature is sufficient to retort spent shale and also pyrolyze coal and to thermally crack excess heavy oil charged to the lower zone as a coal slurry, taking the product as high temperature vapor to a quench tower where the liquid product is recycled to the hydrogenation reactor for hydrogenation and the heavy gas oil is recycled to the slurry mixer.
2. Prior Art
World wide demand for hydrocarbons and related products is continuing at a high annual rate. Crude petroleum and natural gas are basic in satisfying these demands but shortages can be forseen in the near future even though new oil and gas resources are being discovered. Therefore, alternate sources and feed stocks, such as coal, tar sands, oil shale and solid crudes are receiving greater consideration.
Oil shales found in large quantities in various locations throughout the world are an ideal source for obtaining additional quantities of hydrocarbons and related products. Oil shale consists of compacted sedimentary inorganic particles, generally laminated and partly or entirely encased with a high mol. weight organic material called kerogen, which is usually present in amounts of about 6 to 30 percent by wt. of the shale. Kerogen is derived from aquatic organisms or waxy spores and pollen grains, comprising hydrocarbons and complex organix-nitrogen, oxygen and sulfur compounds. Nitrogen in kerogen is largely present in the form of thiophene-type compounds. Crude shale oil produced from the oil shale by pyrolysis of the kerogen differs from crude petroleum by being more unsaturated and having a higher content of nitrogen-compounds. Further, poor color stability and disagreeable odor of the shale products are related to the presence of these compounds.
Prior known methods for recovering oil from raw shale used principally a thermal means and more recently the use of molecular hydrogen. These methods have not been entirely satisfactory as they have generally resulted in a low conversion to the desired high molecular weight liquid products and higher conversion of the kerogen to carbon and gas products which are of low economic value. Furthermore, the desired liquid products have been of low quality in that they have a high molecular weight and contain considerable amounts of the above-described nitrogen, sulfur, and oxygen contaminants. They also differ from the conventional crude oil in having large amounts of unsaturated aliphatic compounds and depending on the shale source little if any aromatics or cyclic compounds. Finally, many of the prior known processes have required the use of considerable amounts of energy and elaborate equipment and are thus very expensive to operate.
Prior known processes for recovering oil shale which have one or more of the above-noted deficiences include: Hoekstra--U.S. Pat. No. 4,414,433, Vasalos--U.S. Pat. No. 4,404,083, Bertelsen--U.S. Pat. No. 4,366,046, Sieg--U.S. Pat. No. 4,293,401, Tarman--U.S. Pat. No. 4,431,509, Hall--U.S. Pat. No. 4,421,603, and Schlinger--U.S. Pat. No. 3,617,470.
Prior known methods involving the addition of coal in such processes include Rankel--U.S. Pat. No. 4,404,091, Rosenthal--U.S. Pat. No. 4,395,983, Arnold--U.S. Pat. No. 3,870,621, Hemminger--U.S. Pat. No. 3,162,583 Hill--U.S. Pat. No. 4,133,742 and Reed--U.S. Pat. No. 3,939,057.
It is an object of the invention, therefore, to provide a new and efficient process for recovering shale oil from raw oil shale. It is a further object to provide a new process for recovering oil from raw oil shale which permits recovery of liquid hydrocarbon products which are more characteristic of conventional crude than possible heretofore. It is a further object to provide a process for recovering oil from raw shale in higher yields than possible heretofore. It is a further object to provide a process for recovering oil from raw shale which has significantly reduced quantities of nitrogen, oxygen and sulfur contaminants. It is a further object to provide a process for recovering oil from raw oil shale which has unusually low heat and energy requirements. It is a further object to provide a process for recovering oil from oil shale which yields large amounts of gas or liquid products for use in the manufacture of its own hydrogen requirements. It is a further object to provide a process utilizing coal char as a low cost supplemental fuel to satisfy total plant energy requirements. It is a further object to provide a process for recovering oil shale which uses equipment compatible with known processes and thus capable of being combined herewith. These and other objects and advantages of the invention will be apparent from the following detailed description thereof.